SVCB: Correctly parse and print unknown params

SVCB: Correctly parse and print unknown params

There were multiple issues. With this commit, we *always* store the
bytes that are represented by the option. To do this, we needed to
properly parse RFC 1035 character-strings. This is now done with a
conversion of the ABNF from draft-ietf-dnsop-svcb-https-02 to ragel.

The resulting function could be used as a starting point for a better
TXT storage format.

(cherry picked from commit b1a048a9caa0d14f9e6665c45af004c041fe5c5e)
(cherry picked from commit ca749ae109941ad0b5e96043b9f6a76305c4fcc7)